In the field of satellite communications, international technical standards, such as the standards defined by the International Telecommunication Union, define recommendations in various sub-fields such as the efficient management of the spectrum or the propagation of electromagnetic waves.
In particular, these standards recommend the observance of certain constraints regarding the equivalent isotropically radiated power density of Earth communication stations transmitting in a satellite communication network. These constraints are defined by a maximum power threshold to be observed by transmitting Earth stations to limit the interference generated on satellites adjacent to the satellite targeted by the station.
The equivalent isotropically radiated power of an Earth station can be computed from the link budget. In other words, it is possible to compute the minimum power at which a station must transmit to comply with a given useful bit rate of transmission and a target signal-to-noise ratio. This computation takes into account the parameters of the waveform of the transmitted signal and the characteristics of the stations of the network as well as those of the satellite. This computation can be performed by resource control equipment to control the transmission power of a signal made by an Earth station via a servo loop.
If the computed power is above the recommended limit, resource control effects a lowering of the bit rate requested of the station so that its power decreases.
To carry out an accurate computation of the equivalent isotropically radiated power, it is necessary to accurately model the various uncertainties of the transmission channel, which requires considerable effort to be expended on calibrating the equipment. Additionally, in the case of mobile Earth stations, notably airborne stations, wide variations in temperature increase the uncertainties on the various gains of the transmission channel. The consequence of these uncertainties is a limitation of the maximum bit rate allocated to a station due to the inaccuracy of the link budget computations. In other words, the computed power setpoint exhibiting a deviation in relation to the power actually transmitted, the resources cannot be allocated optimally to come as close as possible to the maximum authorized power limits.
In other words, when several Earth stations dynamically share the same satellite communication resources, the resource control equipment shares the frequency band between these stations but also the transmissive power. The power sharing is all the more optimal when the transmitted equivalent isotropically radiated power is accurate with respect to the power setpoint given by the resource control equipment. In the opposite case, the resources of the system are not used to their full capability.